Power Automate Approval Attachment Limitations and Restrictions

Per-Attachment Size Limits

The Common Data Service defaults to a per-annotation (attachment) size limit of 5MB, but this can be changed by a CDS environment administrator. To raise this limit:

1. Environment admins should go to the Power Platform Admin center and select the environment that they want to manage.

2. Select "Settings" from the command bar.

3. Select "Email" 

4. In the "Attachments" section update the maximum size in kilobytes.

Please see this link for more information about the Common Data service setting that controls this.

Error Code: CdsApiAttachmentSizeLimitExceeded

Users will see this failure message in flow runs if this limit is being exceeded:

Attachment file size limit exceeded. Please contact your admin to make sure the limit is properly configured (The default is 5MB).'.

The attachment is too large for your CDS instance. The default size is 5MB per file, but this can be configured by database administrators as mentioned above.

Attachment File Type Restrictions

CDS restricts certain file types by extension from being created for security and privacy concerns. It restricts the following file extensions by default:

ade;adp;app;asa;ashx;asmx;asp;bas;bat;cdx;cer;chm;class;cmd;com;config;cpl;crt;csh;dll;exe;fxp;hlp;hta;htr;htw;ida;idc;idq;inf;ins;isp;its;jar;js;jse;ksh;lnk;mad;maf;mag;mam;maq;mar;mas;mat;mau;mav;maw;mda;mdb;mde;mdt;mdw;mdz;msc;msh;msh1;msh1xml;msh2;msh2xml;mshxml;msi;msp;mst;ops;pcd;pif;prf;prg;printer;pst;reg;rem;scf;scr;sct;shb;shs;shtm;shtml;soap;stm;tmp;url;vb;vbe;vbs;vsmacros;vss;vst;vsw;ws;wsc;wsf;wsh

This can be customized by:

1. Environment admins should go to the Power Platform Admin center and select the environment that they want to manage.

2. Select "Settings" from the command bar.

3. Select "Security + Privacy"

4. Under "Blocked Attachments" add or remove file extensions from the semi-colon delimited listed.

Error Code: CdsApiAttachmentBlockedFileExtension

Users will see this failure message in flow runs if an attachment with a restricted file extension was passed to the Approvals action:

'Attachment file extension is blocked. Please contact your admin if changes need to be made to the block list.'.

An administrator in your organization has blocked attachments of the specified type.

Combined Attachment Size Limits

The Approvals connector enforces a 50MB limit on the combined unencoded size of attachments during approval creation. This limit cannot be changed.

Error Code: CdsApiAttachmentBlockedFileExtension

Users will see this failure in flow runs if this limit is exceeded:

The combined attachment size of 68.9MB exceeds the limit of 50MB.'.

The combined size of all attachments unencoded is 68.9MB which exceeds the hard limit of 50MB.

Attachment Naming Restrictions

The Approvals connector only allows attachments with names that do not contain characters such as (but not limited to):  / \ | ? * > < " '

Error Code: InvalidAttachmentName

Users will see this failure in flow runs if this limit is exceeded:

'The attachment name '.*.*.' is invalid.'.

The specified attachment name '.*.*.' is invalid because it contains '*' which is in the list of restricted characters.

Attachment Content Restrictions

The Approvals connector requires attachment content to be encoded in base64 format. Most connector actions that return file data already output the file content in base64. For custom data passed into the attachment parameter, use the base64 expression. Ex: base64(outputs('Get_Attachment'))

Although an empty file is valid base64 content the Approvals connector does not allow empty files as attachments currently due to a limitation with our internal mailing service.

Error Code: AttachmentContentNotValidBase64String

Users will see this failure in flow runs if this limit is exceeded:

'The content for attachment '...' is not a valid base64 encoded string.'.

The attachment content for file '...' must be in base64 format. 

Error Code: AttachmentEmptyContentNotSupported

Users will see this failure in flow runs if this limit is exceeded:

'The content for attachment '...' is empty. Attachments with empty content are not supported.'.

The attachment content for file '...' is empty (0 bytes) which is not allowed at this time.

Approval will only send file attachments on emails automatically sent to approvers if the cumulative attachment size is less than 5MB. Attachments will be available on the Power Automate portal.

Users will see this message in the approval emails when this happens with a link to the Power Automate Approvals Center:

'This approval has attachments that are too big for email.'